Cardioverter defibrillators are medical devices that deliver an electrical shock to the heart via electrodes to terminate arrhythmias. The devices may use the same or a different set of electrodes to monitor electrical heart activity within a patient.
Automated external defibrillators (AEDs) include surface electrodes that are applied to a patient by a paramedic or other trained personnel. Wearable cardioverter defibrillators (WCDs) are personal external monitors that are worn by the patient and contain surface electrodes. The surface electrodes are arranged to provide one or both of monitoring surface electrocardiograms (ECGs) and delivering cardioverter and defibrillator shock therapy.
Implantable cardioverter defibrillators (ICDs) include implantable electrodes. The electrodes are connected to sense amplifiers to provide internal monitoring of a patient's condition. ICDs may include one or more sensors to monitor one or more other internal patient parameters. In other examples, the ICDs are included in a cardiac function management device (CFM) that provides a combination of device capabilities such as pacemaker therapy and cardiac resynchronization therapy (CRT).
Additionally, some medical devices detect events by monitoring electrical heart activity signals. These events can include heart chamber electrical depolarization and the subsequent expansions and contractions. By monitoring cardiac signals indicative of expansions or contractions, medical devices can detect abnormally rapid heart rate, such as tachyarrhythmia. Tachyarrhythmia includes ventricular tachycardia (VT) which originates from the ventricles. Tachyarrhythmia also includes rapid and irregular heart rate, or fibrillation, including ventricular fibrillation (VF). Abnormally rapid heart rate can also be due to supraventricular tachycardia (SVT). SVT is less dangerous to the patient than VT or VF. SVT includes arrhythmias such as atrial tachycardia, atrial flutter, and atrial fibrillation. A rapid heart rate can also be due to sinus tachycardia, which is a normal response to, for example, exercise or an elevated emotional state.
Typically, cardioverter defibrillators detect tachyarrhythmia by first detecting a rapid heart rate. When detected, a tachyarrhythmia can be terminated using cardioversion or defibrillation shock therapy. Other detection methods in addition to fast rate detection are used to reduce the incidence of inappropriate shocks. It is important for cardioverter defibrillators to quickly and accurately classify sensed rhythms or arrhythmias and deliver the appropriate therapy.
An example of a defibrillator with the capability to distinguish pathologic tachycardia from physiologic tachycardia by the application of a predetermined distinction criteria can be found in Alt, “Implantable Medical Interventional Device with Criteria Modification to Enhance Recognition of Tachycardia,” U.S. Pat. No. 5,431,685, filed Jul. 29, 1994. An example of an implantable medical intervention device having an evaluation system to be applied against an ECG signal to recognize pathological tachycardia and distinguish it from physiological tachycardia can be found in Alt, “Device and Method for Automatically Adjusting Tachycardia Recognition Criteria based on Detected Parameter,” U.S. Pat. No. 5,370,667, filed Jul. 20, 1992.